1. Field of the Invention
The present invention relates to a control device of a heater drive apparatus which heats an object.
2. Related Background Art
In a conventional electrophotographic-system image process apparatus, a control device of a heater drive apparatus supplies constant power to a heater in spite of voltage variation of an A/C power supply such that the power consumed by the heater is always kept constant, thereby preventing overshoot and ripple of heater surface temperature. For this reason, a constant voltage output circuit is provided in the heater.
Further, in a case where the image process apparatus uses a halogen heater as a heat source and a lighting fixture to which power is supplied from the same outlet as that for the image process apparatus exists, a flicker phenomenon such as flickering of the lighting fixture or the like occurs since a rapid current fluctuation at the time of turn on/off of the halogen heater occurs depending on a certain power supply impedance. In order to prevent such the phenomenon, an output from the constant voltage output circuit is gradually raised and fallen in a certain time constant to eliminate the rapid current fluctuation.
Furthermore, in a case where plural heaters are connected to one constant voltage output circuit, when a part or all of the plural heaters being in an OFF state are turned on, or on the contrary when the part or all of the heaters in an ON state are turned off, the rapid current fluctuation is eliminated by gradually raising or falling the output from the constant voltage output circuit in the certain time constant.
However, in case of switching or changing connection of a power switch, an excessive voltage is generated due to counter-electromotive force of an inductor, whereby there is some fear that circuit elements are destroyed. In order to prevent such destruction, it is required to perform the switching always after confirming that the output voltage from the constant voltage output circuit once comes to have a value equal to or lower than a predetermined value or after elapsing a sufficient period of time.
Further, a long period of time is necessary until the heater is warmed up.